Piezo Servo Valve Shutter for Compact Fuel Injector
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Solution Overview
Problem
Current servo valves for internal combustion engine fuel injectors using electromagnetic actuators are not compatible with piezoelectric actuators, which can only exert thrust and not pull, leading to complexity and bulkiness when trying to achieve sufficient fuel discharge flow, as they require travel amplification systems or increased sealing areas, resulting in high axial forces and complexity.
Innovation Solution
A servo valve design utilizing a piezoelectric actuator with a control chamber and a shutter that engages an inner seat to form an annular chamber, allowing the shutter to be axially slid from a closed to an open position without axial resultant force from fuel pressure, using a preloaded spring and a compact, low-component structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If piezoelectric actuators are used instead of electromagnetic actuators, then the servo valve can be simplified and made more compact, but piezoelectric actuators can only exert thrust and not pull, limiting their applicability
Solution Approach 1:
The patent inverts the conventional approach by making the shutter the primary sealing element that closes the outlet hole, rather than having a separate closure mechanism. The shutter is subjected to axial thrust from fuel pressure that pushes it against the conical seat for sealing, while the piezoelectric actuator only needs to provide minimal thrust to open it. This inversion allows the piezoelectric actuator's unidirectional thrust capability to be sufficient for the opening action without requiring a separate pull mechanism.
2Volume of moving object
If piezoelectric actuators are used with limited displacement, then the actuator size is reduced, but travel amplification systems or increased sealing area are required to achieve necessary fuel discharge flow
Solution Approach 1:
The patent utilizes the conical geometry of the seat and shutter arrangement to convert minimal axial displacement of the shutter into effective sealing area through geometric relationships. The conical seat creates a progressive sealing area as the shutter moves axially, allowing small axial travel to engage sufficient sealing area for the required fuel discharge flow, eliminating the need for travel amplification systems.
3Productivity
If the sealing area is increased to achieve necessary fuel discharge flow with piezoelectric actuators, then the fuel discharge flow is sufficient, but the axial force from fuel pressure increases requiring higher spring preload
Solution Approach 1:
The patent applies local quality by concentrating the sealing function at the conical seat interface where the shutter makes contact. The conical geometry creates a localized sealing area that provides sufficient fuel discharge flow while the axial thrust is distributed over this specific conical contact zone. This localized sealing approach allows the spring preload to be optimized for the actual sealing requirement rather than requiring excessive force for a larger sealing area.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design enables ample fuel discharge flow with minimal shutter lift, reducing the spring preload by 30% and eliminating the need for travel amplification systems, resulting in a compact, low-cost, and straightforward solution for using piezoelectric actuators in fuel injectors.
Implementation Method 1
actuating means comprising a piezoelectric actuator
Implementation Method 2
the axial thrust of a spring preloaded to keep the outlet hole closed
Data Source
AI summary
A control servo valve (8) is housed inside the casing (2) of an internal combustion engine fuel injector (1), and has a piezoelectric actuator (40), and a control chamber (13) having a fuel outlet passage (21); the outlet passage (21) comes out inside an annular chamber (34) defined by a fixed tubular portion (25) and by a shutter (32), which engages the tubular portion (25) in substantially fluidtight manner and is slid axially by the piezoelectric actuator (40) from a closed position, in which it closes the annular chamber (34) and is subjected to a zero axial resultant force by the fuel pressure, to an open position, in which the outlet passage (21) communicates with a discharge conduit.